However, according to Eq. REF , assuming an uninterrupted accretion (\(f_{duty}=1\) ) at the Eddington rate and a radiative efficiency \(\epsilon =0.1\)  (\(10\%\)  of the material falling towards the BH is converted into radiation, as described by the standard, radiatively efficient, thin-disc accretion model; e.g., [1]}), a light seed of \(100 \, \rm M_\odot \)  barely reaches a mass of \(10^9 M_\odot \)  by \(z=6 (5)\)  if it forms at \(z=30 (20)\)  and can not explain the formation of the most massive QSOs at \(z>6\)  (see Figure REF ).
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